Liquid crystal displays (LCD) have low working voltages, low power consumptions, flexible display modes, and low radiation. Thus, LCDs are widely utilized in various fields, such as fields related to computers, mobile phones, televisions, and measuring equipment displays. LCD includes a liquid crystal display panel and a backlight. The backlight provides a light source to the liquid crystal display panel so that the display panel is able to display images. As shown in FIG. 1 to FIG. 3, the backlight includes a back cover 10, a bezel 20, a mold frame 30, an optical sheet 40, a light guide panel (LGP) 50, a LED light bar 60, and the like. The LED light bar 60 is disposed adjacent to a light incident surface of the light guide panel 50. Lights emitted from the LED light bar 60 enter into the light guide panel 50 via the light incident surface of the light guide panel 50, reflected by a dot pattern disposed at a bottom side of the light guide panel 50 and a reflecting sheet 70, and exit from a light-exiting surface of the light guide panel 50. Then, the lights exit from the light guide panel 50 are diverged and converged by the optical sheet 40 and are exited from the optical sheet 40 as a uniform surface light source. The uniform surface light source provides a light source of the display panel 80.
Usually, the LED light bar 60 of the backlight includes multiple LEDs arranged at predetermined intervals. Each LED has a predetermined light emitting angle (120 degrees). FIG. 2 is a diagram showing a transmission of the lights. As shown in FIG. 2, in the light guide panel 50, areas in which the lights exist become bright areas, and areas to which the lights from two adjacent LED light bars 60 cannot reach become dark areas. Thus, in the areas adjacent to a light incident surface of the light guide panel 50, the bright areas and the dark areas are alternatively generated. That is, hot-spot phenomenon is generated. A generation of the hot-spot phenomenon is affected by the following factors.
First, LED pitch d1: the hot-spot phenomenon is generated more easily when the distance d1 between two adjacent LEDs increases.
Second, a distance d2 between the LED and the light guide panel: the hot-spot phenomenon is generated more easily when the distance d2 decreases.
Third, a package size d3 of the LED (LED PKG): different LED packages, such as 3020 type and 7020 type, have different dimensions (3 mm, 7 mm): under the same conditions, the hot-spot phenomenon is generated more easily in the 3020 type.
Fourth, a distance d4 between the LED and an effective display area (AA area) of the display panel: the hot-spot phenomenon is generated more easily when the distance d4 decreases.
With an improvement in a light emitting efficiency of the LED, the number of LEDs included in the backlight decreases. When the number of LEDs decreases, the hot-spot phenomenon is more likely to be generated. Thinning of the LCD device and narrow border of the LCD device cause a decrease in the distance between the LED and the light guide panel and the distance between the LED and the effective display area of the display panel. By this reason, a LED light mixing distance is not enough, and the hot-spot phenomenon is more easily generated. Usually, before a development of a product, estimation and evaluation of the hot spots are carried out based on experience summarization and an optical simulation software. Since the optical simulation software has its own limitation, the amount of simulated lights is limited (for example, several tens of thousands of lights, several hundreds of thousands of lights). When the amount of simulated lights increase, the time required for the simulation increases (for example, simulation with the server requires 12 minutes in the case of millions of light rays). Seen from this example, the simulation using optical software has its own limitations, and the simulation result also has errors compared with a real sample. Thus, the optical simulation software has a low accuracy and requires a long time for the simulation.